Field of the Invention
Embodiments of the present invention relate to a technique of detecting a muon track.
Related Art
Among techniques of imaging an interior of a structure, techniques of seeing through the interior by observing muons reaching the surface of the Earth have been known. These techniques have been suitably used for large structures into which access is difficult, including, for instance, volcanoes and pyramids.
Among the techniques of seeing through the interior of a structure using muons, transmission methods of measuring attenuation of a muon particle flux, and scattering methods of measuring Coulomb multiple scattering angles of muons have been known. Among the scattering methods, a displacement method of measuring the displacement of a muon track due to Coulomb multiple scattering has been known.
The technique of seeing-through using muons requires a muon tracker provided outside of a structure to be seen through. This tracker detects a muon track, and analyzes this track, thereby imaging the interior of the structure.
The muon tracker includes arrays of drift tubes in which drift gas is sealed are stacked into multiple layers. Anode wire is stretched at the center of each drift tube. When a charged particle, such as a muon, passes through the drift tube, the internally sealed gas is ionized to release electrons. Arrival of the released electrons at the anode wire is detected as transit of a muon.
The drift radius (the distance from the anode wire) can be acquired by converting the drift time until the arrival of electrons at the anode wire. The muon track of one passing muon forms a straight line. Accordingly, the muon tracker detects the muon track by calculating the common tangent of circles having the drift radii.
The calculation of the muon track requires the time in which the muon passes through the drift tube. Conventionally, a detector for measuring the transit time is separately provided in addition to the drift tube to measure the transit time.
Another method has also been known that does not require any detector other than the drift tube, adopts the muon transit time as a variable referred to as “time-zero” and derives the muon track from a condition that the muon track should form a straight line.
Thus, the technique that adopts the muon transit time as a variable referred to as “time-zero” and derives the muon track from the condition that the muon track should form a straight line does not separately require any detector for measuring the transit time of a muon. However, this technique requires complicated calculation for obtaining the muon transit time. Accordingly, for instance, it is difficult to detect the muon track in real time.